Your average rock, tree, or branch will never appear harmless after “Lone Survivor.” With its depiction of warfare in Afghanistan moved to the unlikely setting of evergreens and jagged cliffs, the most horrific moments of director Peter Berg’s drama come from a body in free fall—and its eventual landing upon each. Never mind the fact that surrounding Taliban forces rain gunfire and RPGs down upon four injured American soldiers out on a recon mission; nature is the true enemy, and the extent of its cruelty is explored to the fullest over the course of the film’s harrowing two hours.

Your average rock, tree, or branch will never appear harmless after “Lone Survivor.” With its depiction of warfare in Afghanistan moved to the unlikely setting of evergreens and jagged cliffs, the most horrific moments of director Peter Berg’s drama come from a body in free fall—and its eventual landing upon each. Never mind the fact that surrounding Taliban forces rain gunfire and RPGs down upon four injured American soldiers out on a recon mission; nature is the true enemy, and the extent of its cruelty is explored to the fullest over the course of the film’s harrowing two hours.

Bookended by lengthy documentary snapshots of Navy SEALs—a montage from boot camp to graduation over the opening titles, then an In Memoriam for 19 U.S. soldiers during the end—the film is foremost a tribute, based off of Marcus Luttrell’s 2009 non-fiction book “Lone Survivor.” We see soldiers, including the then 29-year-old Texan Luttrell (played by Mark Wahlberg), Lt. Michael Murphy (Taylor Kitsch), Danny P. Dietz (an underused Emile Hirsch), and Technician Matthew Axelson (Ben Foster), but they are always ciphers—reminders of the real-life SEALs that embarked upon a quickly doomed mission in 2005 to capture or kill Taliban head Ahmad Shah (Yousuf Azami).

Not that the surface level characters are necessarily an issue. Berg needs only relatable eyes through which to immerse us into the later battle. Worryingly, he does this quickly, and with a maximum of broad clichés and shortcuts: Foster gazes at a picture of his wife as he IMs her on his computer, Lt. Commander Kristensen (Eric Bana) makes fun of the new recruit (Alexander Ludwig), while Hirsch jokingly describes to Wahlberg and Kitsch his significant other’s ideas for interior decorating. However accurate the background detail, the approach comes off as Mad Libs motivation, and alongside the constantly booming score by Explosions In The Sky and Steve Jablonsky, subtlety sneaks out the door early on.

These early scenes do showcase a rare success though, one that sustains itself through most of the film: Taylor Kitsch. Berg’s man from his previous film “Battleship,” the “John Carter” actor finds an impressive groove early on as Lt. Murphy, a competitive personality fixed on practicality. This ability factors in crucially when, as the soldiers idle on the Afghanistan mountains at the start of their mission, a group of goat herders stumble upon the operation. Suddenly Luttrell and co. are faced with the choice of killing these unarmed civilians in cold blood, or freeing them with the knowledge that they’ll notify the Taliban immediately afterwards.

The ensuing discussion is tense and well acted, with no easy outcome. Here, Wahlberg steps in as full audience gateway, his guiding eyes and amiable craft capturing the impossible conflict that he and his team must overcome. His is not the best performance in the film; that honor goes to Foster, who humanizes Axelson with a full-spirited passion and sensitive humor. But together, all four cast members help draw a line across the narrative—separating when we were watching a mildly engaging depiction of names, dates, and locations, and a hellish, immersive situation with no easy outcome in sight.

Once the 150-strong Taliban forces eventually spot Luttrell and his team, the film transfers into a vicious, sustained firefight, and also its most successful scenes. By “successful,” we mean so visceral and agonizing that our eyes had to look away from the screen almost every few minutes. A succinct death for any of our main characters would be a godsend; rather, they are ripped to shreds by bullets, impaled on tree branches, and bludgeoned on rocks repeatedly over 45 minutes before a bloody end finally comes. Greg Nicotero, working on the special prosthetic effects here with Howard Berger, turns in consistently excellent work; one begins to hate him for the achievement.

Alternating between stunning overhead views of the firefight lensed by Tobias Schliesser and the handheld chaos within it, Berg—a talented stager of action as “The Kingdom” and “The Rundown” show—also chooses to cut away to the momentum-killing efforts of Lt. Cmdr. Kristensen staging a rescue operation. As a result, we never get a sense of just how long the entire skirmish lasts; it could be one day or three, until a title card appears to properly tell us otherwise.

We also get unneeded detail on the Taliban enemy—only witnessed so a late-stage threat of a beheading can evoke a gruesome callback. Presenting Shah as an eternally scowling military leader whose main trait is that he has no earlobes, Berg is content to let a propagandistic edge seep into what is already a boldly patriotic film. In turn, this tips the narrative over into black-and-white portrayals that cheapen it significantly.

Berg attempts to balance the situation later on by focusing on the sympathetic conduct of the native Pashtun people, but by then the director has already started the catharsis for America’s military efforts. Because of its hugely immersive central battle, that element can be tolerated as long as you expect “Lone Survivor” not to provoke questions outside of bravery and sacrifice. As it fades out though, it remains a deeply intense, detached museum piece—hosting a small, intriguing plaque that might lead you to the denser story elsewhere, if you so wish. [B]